just wanting to ask, are alien weapons affective against normal ships as well as alien ships? just asking before i start into the alien galaxy. yes i know i need the alien weapons there but what about in other places?

Err, you do not need Plasma weapons to kill Aliens. Kinetic works excellent. And Plasma guns can kill normal ships. They are too strong for raids, however.
But
You need Plasma salvage gear to salvage Alien Wrecks, and you cannor salvage regular wrecks with Plasma salvage guns. And salvage in expanse is really important.

There are also Alien Derelicts, where you need energy or Plasma guns, but it is rarely useful